Nickel base superalloy compositions being substantially free of rhenium and superalloy articles

ABSTRACT

A nickel base superalloy composition substantially free of rhenium includes, in percentages by weight: about 5-8 Cr; about 7-8 Co; about 1.3-2.2 Mo; about 4.75-6.75 W; about 6.0-7.0 Ta; if present, up to about 0.5 Ti; about 6.0-6.4 Al; about 0.15-0.6 Hf; if present, from about 0.03-0.06 C; if present, up to about 0.004 B; if present, one or more rare earths selected from Y, La, and Ce up to about 0.03 total, the balance including nickel and incidental impurities. The superalloy composition is able to provide sustained-peak low cycle fatigue and/or oxidation resistance properties comparable to second generation superalloy compositions including at least about 3 wt % rhenium. Superalloy articles incorporating the compositions include nozzles, shrouds, and splash plates for gas turbine engines.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application claims priority to U.S. Provisional Application Ser. No. 60/969,360, filed Aug. 31, 2007, which is herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

Embodiments disclosed herein pertain generally to nickel base superalloys and articles of manufacture comprising nickel base superalloys. Disclosed embodiments may be utilized for components disposed in hot sections of a gas turbine engine, and more particularly for use in non-creep limited applications, such as turbine nozzles and shrouds.

BACKGROUND OF THE INVENTION

The efficiency of gas turbine engines depends significantly on the operating temperature of the various engine components with increased operating temperatures resulting in increased efficiencies. The search for increased efficiencies has led to the development of superalloys capable of withstanding increasingly higher temperatures while maintaining their structural integrity.

Nickel-base superalloys are used extensively throughout the aeroengine in turbine blade, nozzle, and shroud applications. Aeroengine designs for improved engine performance require alloys with increasingly higher temperature capability. Although shroud and nozzle applications do not require the same level of high temperature creep resistance as blade applications, they do require similar resistance to thermal mechanical failure and environmental degradation. Superalloys are used for these demanding applications because they maintain their strength at up to 90% of their melting temperature and have excellent environmental resistance.

Single crystal (SC) superalloys may be divided into “four generations” based on similarities in alloy composition and performance. A defining characteristic of so-called “first generation” SC superalloys is the absence of the alloying element rhenium (Re). For example, U.S. Pat. Nos. 5,154,884; 5,399,313; 4,582,548; and 4,209,348 each discloses superalloy compositions substantially free of Re.

A representative SC nickel-base superalloy is known in the art as Rene N4 having a nominal composition of: 6.0-7.0% Co, 9.5-10.0% Cr, 1.5% Mo, 6.0% W, 4.8% Ta, 4.2% Al, 3.5% Ti, 0.5% Nb, 0.01 maximum % B, 0.2 maximum % Hf, and balance essentially Ni and C wherein C is specified as 0.01% (100 ppm) maximum. Mach 1 velocity cyclic oxidation Test at 2150° F. data for a Rene N4 superalloy and an AM1 superalloy are provided for comparative purposes in the accompanying Figures.

It was discovered that the addition of about 3 wt % Re to superalloy compositions provides about a 50° F. (28° C.) improvement in rupture creep capability and the accompanying fatigue benefits. Production alloys such as CMSX-4, PWA-1484 and Rene N5 all contain about 3 wt % Re. These “second-generation” alloys are disclosed, for example, in U.S. Pat. Nos. 4,719,080; 4,643,782; 6,074,602 and 6,444,057.

U.S. Pat. No. 4,719,080 provides a relationship between compositional elements called a “P-value” defined as P=−200 Cr+80 Mo−20 Mo²−250 Ti²−50 (Ti×Ta)+15 Cb+200 W−14 W²+30 Ta²−1.5 Ta²+2.5 Co+1200 Al+100 Al²+100 Re+1000 Hf−2000 Hf²+700 Hf³−2000 V−500 C−15000 B−500 Zr. The patent stresses that a higher “P-value” correlates with high strength in combination with stability, heat treatability, and resistance to oxidation and corrosion. In particular, the superalloy compositions disclosed in the patent are constrained by “P-values” greater than 3360.

U.S. Pat. No. 6,074,602 is directed to nickel-base superalloys suitable for making single-crystal castings. The superalloys disclosed therein include, in weight percentages: 5-10 Cr, 5-10 Co, 0-2 Mo, 3-8 W, 3-8 Ta, 0-2 Ti, 5-7 Al, up to 6 Re, 0.08-0.2 Hf, 0.03-0.07 C, 0.003-0.006 B, 0.0-0.04 Y, the balance being nickel and incidental impurities. These superalloys exhibit increased temperature capability, based on stress rupture strength and low and high cycle fatigue properties, as compared to the first-generation nickel-base superalloys. Further, the superalloys exhibit better resistance to cyclic oxidation degradation and hot corrosion than first-generation superalloys.

U.S. Pat. Nos. 5,151,249; 5,366,695; 6,007,645 and 6,966,956 are directed to third- and fourth-generation superalloys. Generally, third-generation superalloys are characterized by inclusion of about 6 wt % Re; fourth generation superalloys include about 6 wt % Re, as well as the alloying element Ru. These superalloy compositions illustrate the value of increased Re additions in terms of mechanical performance.

First generation SC superalloys do not offer the thermal mechanical failure (TMF) resistance or the environmental resistance required in many hot section components such as turbine nozzles and shrouds. Also, first-generation SC superalloys do not offer acceptable high temperature oxidation resistance for these components.

Currently, aeroengines predominantly use second-generation type superalloys in an increasing number of hot section applications. The alloying element Re is the most potent solid solution strengthener known for this class of superalloys and therefore it has been used extensively as an alloying addition in SC and columnar-grained directionally solidified (DS) superalloys. The second-generation superalloys exhibit exceptional high temperature oxidation capability balanced with satisfactory mechanical properties.

Known superalloy compositions having lower Re content have not been able to provide the properties obtainable from second-generation superalloys. In particular, in U.S. Pat. No. 4,719,080, the data for one alloy (namely, B1) having less than 2.9% Re show properties comparable to first-generation, i.e., no Re, superalloys. Thus, in the development of superalloy compositions, the trend has been to use at least 3 wt % Re to obtain a satisfactory balance of oxidation resistance and high temperature strength.

However, the cost of the raw materials, and the global shortage of Re in particular, provides a challenge to develop superalloy compositions able to provide the demonstrated improved mechanical properties and oxidation resistance of second generation superalloys, but at low, and preferably 0% Re levels.

Accordingly, it would be desirable to provide nickel-base superalloy compositions being substantially free of rhenium that are able to provide desired high temperature mechanical properties and oxidation resistance.

BRIEF DESCRIPTION OF THE INVENTION

The above-mentioned need or needs may be met by exemplary embodiments which provide nickel-base superalloy compositions able to provide the desired thermal mechanical properties, creep strength, and oxidation resistance with substantially no Re content.

An exemplary embodiment provides a nickel base superalloy composition including, in percentages by weight: about 5-8 Cr; about 7-8 Co; about 1.3-2.2 Mo; about 4.75-6.75 W; about 6.0-7.0 Ta; if present, up to about 0.5 Ti; about 6.0-6.4 Al; if present, up to about 1.3 Re; about 0.15-0.6 Hf; if present, from about 0.03-0.06 C; if present, up to about 0.004 B; if present, one or more rare earths selected from Y, La, and Ce up to about 0.03 total, the balance being nickel and incidental impurities.

An exemplary embodiment provides a nickel base single-crystal article comprising a superalloy including, in percentages by weight: about 5-8 Cr; about 7-8 Co; about 1.3-2.2 Mo; about 4.75-6.75 W; about 6.0-7.0 Ta; if present, up to about 0.5 Ti; about 6.0-6.4 Al; if present, up to about 1.3 Re; about 0.15-0.6 Hf; if present, from about 0.03-0.06 C; if present, up to about 0.004 B; if present, one or more rare earths selected from Y, La, and Ce up to about 0.03 total, the balance being nickel and incidental impurities.

An exemplary embodiment provides a gas turbine engine component cast from a nickel base superalloy composition comprising: about 5-8 Cr; about 7-8 Co; about 1.3-2.2 Mo; about 4.75-6.75 W; about 6.0-7.0 Ta; if present, up to about 0.5 Ti; about 6.0-6.4 Al; if present, up to about 1.3 Re; about 0.15-0.6 Hf; if present, from about 0.03-0.06 C; if present, up to about 0.004 B; if present, one or more rare earths selected from Y, La, and Ce up to about 0.03 total, the balance being nickel and incidental impurities.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding part of the specification. The invention, however, may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:

FIG. 1 is a graphical representation of comparative sustained-peak low cycle fatigue (SPLCF) properties.

FIG. 2 is a graphical representation of comparative Mach 1 Velocity Cyclic Oxidation Test data at 2150° F.

FIG. 3 is a graphical representation of comparative Mach 1 Velocity Cyclic Oxidation Test data at 2000° F.

FIG. 4 is a graphical representation of comparative Mach 1 Velocity Cyclic Oxidation Test data at 2150° F.

FIG. 5 is a graphical representation of creep rupture data at 2100° F./10 ksi, normalized to a second-generation nickel base superalloy having about 3 wt % Re content.

FIG. 6 is a graphical representation of creep rupture data at 1600° F., 1800° F., 2000° F., and 2100° F., normalized to a second-generation nickel base superalloy having about 3 wt % Re.

FIG. 7 is a graphical representation of SPLCF data at 2000° F. and 1600° F., normalized to a second-generation nickel base superalloy having about 3 wt % Re.

FIG. 8 is a graphical representation of SPLCF data at 2000° F., normalized to a second-generation nickel base superalloy having about 3 wt % Re.

FIG. 9 is a schematic representation of an exemplary gas turbine engine turbine blade.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views, FIG. 9 depicts a component article 20 of the gas turbine engine, illustrated as a gas turbine blade 22. The gas turbine blade 22 includes an airfoil 24, and attachment 26 in the form of the dovetail to attach the gas turbine blade 22 to the turbine disc (not shown), and a laterally extending platform 28 intermediate the airfoil 24 and the attachment 26. In one exemplary embodiment, a component article 20 is substantially a single crystal. That is, the component article 20 is at least about 80% by volume, and more preferably at least about 95% by volume, a single grain with a single crystallographic orientation. There may be minor volume fractions of other crystallographic orientations and also regions separated by low-angle boundaries. The single-crystal structure is prepared by the directional solidification of an alloy composition by methods known to those with skill in the art. In another exemplary embodiment, the component article 20 is a directionally oriented poly-crystal, in which there are at least several grains all with a commonly oriented preferred growth direction.

The alloy composition discussed herein may be employed in other gas turbine engine components such as nozzles, shrouds, and splash plates.

Embodiments disclosed herein balance the contributions of various alloying elements to the thermal mechanical properties, creep strength, and oxidation resistance of the compositions while minimizing detrimental effects. All values are expressed as a percentage by weight unless otherwise noted.

For example, certain embodiments disclosed herein include at least about 5% chromium (Cr). Amounts less than about 5% may reduce the hot corrosion resistance. Amounts greater than about 8% may lead to topologically close-packed (TCP) phase instability and poor cyclic oxidation resistance.

Certain embodiments disclosed herein include at least about 7% to about 8% Co. Lower amounts of cobalt may reduce alloy stability. Greater amounts may reduce the gamma prime solves temperature, thus impacting high temperature strength and oxidation resistance.

Certain embodiments disclosed herein include molybdenum (Mo) in amounts from about 1.3% to 2.2%. The minimum value is sufficient to impart solid solution strengthening. Amounts exceeding the maximum may lead to surface instability. Greater amounts of Mo may also negatively impact both hot corrosion and oxidation resistance.

Certain embodiments disclosed herein include tungsten (W) in amounts from about 4.75% to about 6.75%. Lower amounts of W may decrease strength. Higher amounts may produce instability with respect to TCP phase formation. Higher amounts may also reduce oxidation capability.

Certain embodiments disclosed herein may include tantalum (Ta) in amounts from about 6.0% to about 7.0%. Other embodiments may include Ta in amounts from about 6.25% to about 6.5%.

Certain embodiments disclosed herein may include aluminum (Al) in amounts from about 6.0% to about 6.5%. Other embodiments may include from about 6.2% to about 6.5% Al.

Certain embodiments disclosed herein may optionally include up to about 0.5% titanium (Ti). Titanium is a potent gamma prime hardener. The optional Ti addition can strengthen the gamma prime phase, thus improving creep capability. However, oxidation resistance can be adversely affected by the addition of Ti, especially at levels greater than about 0.5%.

In an exemplary embodiment, a superalloy composition includes substantially no Re content. By “substantially no Re content” it is meant that Re additions are not nominally called for in an exemplary composition. However, it is envisioned that compatible revert alloy (i.e., used, scrap, or otherwise reclaimed, alloy) may be utilized to provide exemplary superalloy compositions. In such embodiments, Re may be present in amounts up to about 1.3%.

Certain embodiments disclosed herein include hafnium (Hf) in amounts of from about 0.15% to about 0.6%. Hafnium is utilized to improve the oxidation and hot corrosion resistance of coated alloys and can improve the life of an applied thermal barrier coating. Hafnium additions of about 0.7% can be satisfactory, but additions of greater than about 1% adversely impact stress rupture properties and the incipient melting temperature.

Certain embodiments disclosed herein may include up to about 0.004% boron (B). B provides strains for low angle boundaries and enhanced acceptability limits for components having low angle grain boundaries.

Carbon (C), if present, may be included in amounts of from about 0.03% to about 0.06%. The lower limit provides sufficient C to allow for a cleaner melting alloy and to aid in promoting corrosion resistance.

Rare earth additions, i.e., yttrium (Y), lanthanum (La), and cerium (Ce), may be optionally provided in certain embodiments in amounts up to about 0.03%. These additions may improve oxidation resistance by enhancing the retention of the protective alumina scale. Greater amounts may promote mold/metal reaction at the casting surface, increasing the component inclusion content.

An exemplary embodiment includes a nickel base superalloy comprising, in weight percent, a nominal composition comprising: 6.0 Cr, 7.5 Co, 1.5-2.0 Mo, 6.0-6.5 W, 6.5 Ta, 0 Ti, 6.2 Al, 0 Re, 0.15 to 0.6 Hf, 0.03-0.06 C, 0.004 B, the balance being nickel and incidental impurities. Certain exemplary embodiments are further characterized by P-values of less than 3360, wherein the P-values are determined in accordance with the relationship provided above. In exemplary embodiments, the P-values are less than 3250.

Table 1 below provides an exemplary composition series and associated Re ratios and P-values. The “Re Ratio” is defined herein as the ratio of wt % Re to the total of wt % W plus wt % Mo. For exemplary embodiments comprising substantially no Re, the Re ratio is essentially zero (e.g., alloys 1-4, 15 and 16). The values for each composition are given in weight %, the balance being nickel and incidental impurities. For comparative purposes, a nominal composition, Re ratio, and P value is provided for Rene N5.

Table 2 below provides another exemplary composition series, associated Re ratios, and Creep Rupture (CR) data, normalized to a second-generation (i.e. 3% Re) nickel base superalloy. The exemplary compositions in Table 2 provide compositions having about 1 wt % Re which are able to provide desired creep rupture strength. Data from Table 2 as compared to a second-generation alloy (3 wt % Re) and a first generation alloy (0 wt % Re) is presented in FIG. 8.

TABLE 1 Re P- Alloy Al Ta Cr W Mo Re Co C B Hf Ratio Value R N5 6.2 6.5 7 5 1.5 3 7.5 0.05 0.004 0.15 0.46 3069 1 6.2 6.5 6 6 1.5 0 7.5 0.03 0.004 0.15 0.00 3025 2 6.2 6.5 6 6 2 0 7.5 0.03 0.004 0.15 0.00 3030 3 6.2 6.5 6 6.5 1.5 0 7.5 0.03 0.004 0.15 0.00 3037 4 6.2 6.5 6 6.5 2 0 7.5 0.03 0.004 0.15 0.00 3042 5 6.2 6.5 6 6 1.5 1.5 7.5 0.03 0.004 0.15 0.20 3175 6 6.2 6.5 6 6 1.5 2 7.5 0.03 0.004 0.15 0.27 3225 7 6.2 6.5 6 6 2 2 7.5 0.03 0.004 0.15 0.25 3230 8 6.2 6.5 6 6 2 1.5 7.5 0.03 0.004 0.15 0.19 3180 9 6.2 6.5 6 6.5 1.5 1.5 7.5 0.03 0.004 0.15 0.19 3187 10 6.2 6.5 6 6.5 1.5 2 7.5 0.03 0.004 0.15 0.25 3237 11 6.2 6.5 6 6.5 2 2 7.5 0.03 0.004 0.15 0.24 3242 12 6.2 6.5 6 6.5 2 1.5 7.5 0.03 0.004 0.15 0.18 3192 13 6.2 6.5 6 6 1.5 1.5 7.5 0.03 0.004 0.6 0.20 3099 14 6.2 6.5 6 6.5 2 1.5 7.5 0.03 0.004 0.6 0.18 3116 15 6.2 6.5 6 6.5 1.5 0 7.5 0.03 0.004 0.6 0.00 2961 16 6.2 6.5 6 6 2 0 7.5 0.03 0.004 0.6 0.00 2954

TABLE 2 Re N. CR Alloy Al Ta Cr W Mo Re Co C B Ti Ratio (hrs)  1A 6.2 7 6 6.5 1.75 1 7.3 0.04 0.004 0.3 0.14 1.03  2A 6.2 6.5 6 6.5 2.25 1 7.3 0.04 0.004 0 0.18 1.05  3A 6.2 7 6 6 2.25 1 7.3 0.04 0.004 0 0.19 1.06  4A 6.2 6 6 6.5 2.25 1 7.3 0.04 0.004 0.3 0.18 1.06  5A 6.2 6.5 6 6 2.25 1 7.3 0.04 0.004 0.3 0.19 1.10  6A 6.2 7 6 5.5 2.25 1 7.3 0.04 0.004 0.3 0.20 1.10  7A 6.2 6.5 6 6.5 2 1 7.3 0.04 0.004 0.3 0.16 1.11  8A 6.2 7 6 6 2 1 7.3 0.04 0.004 0.3 0.17 1.12  9A 6.2 7 6 6.5 2.25 1 7.3 0.04 0.004 0 0.18 1.21 10A 6.2 6.25 6.4 6.5 2.25 1 7.5 0.04 0.004 0.3 0.17 1.25 11A 6.2 6.5 6 6.5 2.25 1 7.3 0.04 0.004 0.3 0.18 1.27 12A 6.2 7 6 6.5 2 1 7.3 0.04 0.004 0.3 0.16 1.30 13A 6.2 7 6 6 2.25 1 7.3 0.04 0.004 0.3 0.19 1.35 14A 6.2 7 6.4 6.5 2.25 1 7.5 0.04 0.004 0.3 0.17 1.38 15A 6.2 7 6.4 6 2.25 1 7.5 0.04 0.004 0 0.18 1.40 16A 6.2 6.5 6.4 6.5 2.25 1 7.5 0.04 0.004 0.3 0.17 1.46 17A 6.2 7 6 6.5 2.25 1 7.3 0.04 0.004 0.3 0.18 1.62

FIG. 1 illustrates the improved sustained-peak low cycle fatigue (SPLCF) properties of certain embodiments disclosed herein that are beyond that of first-generation superalloys, and more comparable to second-generation superalloys. First generation SC superalloys do not offer thermal mechanical failure (TMF) resistance required in many hot section components. SPLCF is driven by a unique combination of properties, one of which is oxidation resistance. SPLCF or TMF capability is important for cooled hardware because of the temperature gradient within the part.

FIG. 2 provides a comparative graphical representation of data showing weight loss over time during a Mach 1 Velocity Cyclic Oxidation Test at 2150° F., illustrating improved oxidation resistance for certain embodiments disclosed herein.

FIG. 3 provides a comparative graphical representation of data showing weight loss over time during a Mach 1 Velocity Cyclic Oxidation Test at 2000° F., illustrating improved oxidation resistance for certain embodiments disclosed herein.

FIG. 4 provides a comparative graphical representation of data showing weight loss over time during a Mach 1 Velocity Cyclic Oxidation Test at 2000° F., illustrating improved oxidation resistance for certain embodiments disclosed herein.

FIG. 5 is a graphical representation of creep rupture data at 2100° F./10 ksi, normalized to a second-generation nickel base superalloy having about 3 wt % Re content. Certain embodiments disclosed herein compare favorably with the second-generation superalloys, and exhibit marked improvement over first-generation superalloys. It is believed that stability of the gamma prime phase, especially at temperatures in excess of 2100° F., contributes to the improved properties. In certain of the compositions disclosed herein, the volume fraction of the gamma prime phase at 2150° F. is about 46%, comparable to second-generation superalloys, and generally greater than first-generation superalloys. The relative stability of the gamma prime phase benefits the SPLCF resistance and positively affects the creep rupture properties at 2100° F.

Creep rupture data, normalized to a second-generation nickel base superalloy illustrate that embodiments disclosed herein having low Re content are more comparable to second-generation superalloys than first-generation superalloys. Normalized creep rupture data at 1600° F., 1800° F., 2000° F., and 2100° F. for alloy 5-alloy 14 (Table 1) is provided in FIG. 6.

FIG. 7 is a graphical representation of SPLCF data at 2000° F. and 1600° F., normalized to a second-generation nickel base superalloy having about 3 wt % Re.

FIG. 8 is a graphical representation of SPLCF data at 2000° F., normalized to a second-generation nickel base superalloy having about 3 wt % Re.

Superalloy compositions disclosed herein may be utilized to produce single crystal articles having temperature capability on par with articles made from second-generation superalloys. An article so produced may be a component for a gas turbine engine. Such an article may be an airfoil member for a gas turbine engine blade or vane. The article so produced may be a nozzle, shroud, splash plate, or other high temperature component.

Certain exemplary embodiments disclosed herein may be especially useful when directionally solidified as hot-section components of aircraft gas turbine engines, particularly rotating blades.

A method for producing any of the articles of manufacture disclosed herein includes preparing a nickel base single crystal superalloy element material having a chemical composition as set forth in the disclosed embodiments, from raw materials containing nickel, cobalt, chromium, molybdenum, tungsten, aluminum, tantalum, optionally titanium, substantially 0 wt % rhenium, hafnium, optionally carbon, optionally one or more of yttrium, cesium, and lanthanum. The superalloy element material is subjected to suitable heat treatment and suitable subsequent casting processes. Alternate embodiments include substituting revert superalloy material for at least a portion of the raw materials. Thus, embodiments nominally reciting no Re content may include up to about 1.3 wt % Re upon use of revert material.

Thus, superalloy compositions disclosed herein provide the desired thermal mechanical properties, creep strength, and oxidation resistance with reduced Re content by balancing the contributions of compositional elements.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

1. A nickel base superalloy composition consisting of, in percentages by weight: about 5-6 Cr; about 7-8 Co; about 1.5 Mo; about 6 W; about 6.0-7.0 Ta; if present, up to about 0.5 Ti; about 6.0-6.4 Al; about 0.15-0.6 Hf; if present, from about 0.03-0.06 C; if present, up to about 0.004 B; if present, one or more rare earths selected from Y, La, and Ce up to about 0.03 total; wherein the superalloy composition is substantially free of Re and exhibits a sustained-peak low cycle fatigue resistance exceeding 10,500 cycles to failure at 2000° F./18 ksi APS; the balance of the superalloy composition being nickel and incidental impurities.
 2. The nickel base superalloy composition according to claim 1 being characterized by a P-value of less than 3360, wherein the P-value is defined as: P=−200 Cr+80 Mo−20 Mo²−250 Ti²−50 (Ti×Ta)+15 Cb+200 W−14 W²+30 Ta−1.5 Ta²+2.5 Co+1200 Al −100 Al²+100 Re+1000 Hf−2000 Hf²+700 Hf³−2000 V−500 C−15000 B−500 Zr.
 3. The nickel base superalloy composition according to claim 2 being characterized by a P-value of less than
 3050. 4. The nickel base superalloy composition according to claim 1 wherein the superalloy composition is in the form of a single crystal article.
 5. The nickel base superalloy composition according to claim 4, wherein the single crystal article is a gas turbine engine component chosen from the group consisting of a nozzle, a shroud, and a splash plate.
 6. The nickel base superalloy composition according to claim 1 having a nominal composition, in wt %: 6.2 Al, 6.5 Ta, 6 Cr, 6 W, 1.5 Mo, 0 Re, 7.5 Co, 0.03 C, 0.004 B, 0.15 Hf, the remainder being nickel and incidental impurities.
 7. (canceled)
 8. The nickel base superalloy composition according to claim 12 having a nominal composition, in wt %: 6.2 Al, 6.5 Ta, 6 Cr, 6.5 W, 1.5 Mo, 0 Re, 7.5 Co, 0.03C, 0.004 B, 0.15 Hf, the remainder being nickel and incidental impurities. 9-10. (canceled)
 11. The nickel base superalloy composition according to claim 14 having a nominal composition, in wt %: 6.2 Al, 6.5 Ta, 6 Cr, 6 W, 2 Mo, 0 Re, 7.5 Co, 0.03 C, 0.004 B, 0.6 Hf, the remainder being nickel and incidental impurities.
 12. A nickel base superalloy composition consisting of, in percentages by weight: about 5-6 Cr; about 7-8 Co; about 1.5 Mo; about 6.5 W; about 6.0-7.0 Ta; if present, up to about 0.5 Ti; about 6.0-6.4 Al; about 0.15-0.6 Hf; if present, from about 0.03-0.06 C; if present, up to about 0.004 B; if present, one or more rare earths selected from Y, La, and Ce up to about 0.03 total; wherein the superalloy composition is substantially free of Re and exhibits a sustained-peak low cycle fatigue resistance exceeding 2000 cycles to failure at 1600° F./70 ksi APS; the balance of the superalloy composition being nickel and incidental impurities.
 13. The nickel base superalloy composition according to claim 12 wherein, wherein the superalloy composition is in the form of a single crystal article.
 14. A nickel base superalloy composition consisting of: about 5-6 Cr; about 7-8 Co; about 2 Mo; about 6 W; about 6.0-7.0 Ta; if present, up to about 0.5 Ti; about 6.0-6.4 Al; about 0.6 Hf; if present, from about 0.03-0.06 C; if present, up to about 0.004 B; if present, one or more rare earths selected from Y, La, and Ce up to about 0.03 total; wherein the superalloy composition is substantially free of Re and exhibits a sustained-peak low cycle fatigue resistance exceeding 10,500 cycles to failure at 2000° F./18 ksi APS; the balance of the superalloy composition being nickel and incidental impurities.
 15. The nickel base superalloy composition according to claim 14, wherein the superalloy composition is in the form of a single crystal article.
 16. (canceled)
 17. The nickel base superalloy composition according to claim 15, wherein the single crystal article is a gas turbine engine component chosen from the group consisting of a nozzle, a shroud, and a splash plate.
 18. The nickel base superalloy composition according to claim 13, wherein the single crystal article is a gas turbine engine component chosen from the group consisting of a nozzle, a shroud, and a splash plate. 19-20. (canceled) 